1. Field of the invention
This invention relates to automatically operated closures for flues or ducts in heating systems, and in particular, to a draft closure for flues of the type found in oil or gas fired heating systems and the like.
2. Description of the Prior Art
The prior art, as exemplified by U.S. Pat. Nos. 2,165,488, 2,224,705, 2,633,299, 2,856,992, 3,010,451, and 3,090,558, contains a number of automatically operated damper systems for exhaust stacks in heating systems. The prior art automatically operated damper systems can generally be characterized as having one of more deficiencies, such as being unduly complex, too expensive in requiring unnecessary components, and not being fail-safe; fail-safe being defined as preventing burner operation in the event of failure of the damper to open.
Additionally, prior art heating systems employing automatically operated dampers have generally not been fail-safe and/or not capable of obtaining optimum fuel savings.